2-Substituted benzo[b]thiophenes are compounds of value as synthetic intermediates for drugs, agricultural chemicals and functional polymers.
The hitherto known production processes for 2-substituted benzo[b]thiophenes, for example 2-acetylbenzo[b]thiophene, are as follows.
(1) The process comprising reacting benzo[b]thiophene with butyllithium and further with N,N-dimethylacetamide ##STR3##
(2) The process comprising reacting sodium salt of 2-mercaptobenzaldehyde with chloroacetone in the presence of sodium hydroxide ##STR4##
(3) The process comprising reducing thiosalicylic acid with lithium aluminum hydride to lithium salt of 2-mercaptobenzyl alcohol, then reacting it with chloroacetone to give the sulfide and cyclizing the same with pyridine-sulfur trioxide ##STR5##
However, each of these known processes has the following disadvantages.
The process (1) cannot be commercially profitable because of the high cost of the starting material benzo[b]thiophene.
The process (2) has problems in connection with the production of the starting material 2-mercaptobenzaldehyde or corresponding alkali metal mercaptide as well as in the stability of those compounds.
The process (3), like the process (1), involves the use of expensive starting and auxiliary materials and, as such, cannot be commercially profitable.